/Engine/Source/Editor/AssetDefinition/Public/AssetDefinition.h
This category is special, "Basic" assets appear at the very top level and are not placed into any submenu. Arguably the basic category should not exist and should instead be user configurable on what they feel should be top level assets.
static [FAssetCategoryPath](API\Editor\AssetDefinition\Misc\FAssetCategoryPath) Basic;